All suspension systems for wheeled vehicles are designed to operate within a given range of travel or articulation. As a wheeled vehicle moves over a road or other surface, the wheels continually encounter irregularities in those surfaces that result in forces being transmitted to the vehicle suspension system. The vehicle's suspension system, therefore, must be able to articulate up and down in the vertical plane from its designed ride height, to accommodate irregularities in the road surface. Although it is important to allow this articulation of the suspension system, it is equally important to provide some type of positive restraint on the maximum amount of allowable travel in both upward and downward directions, to assure that suspension parameters are not exceeded, and thereby prevent any resultant damage to the suspension system components or the vehicle itself. Air spring damage may occur, for example, if the stroke of the suspension is not limited and the air spring is overextended. Limitation of downward travel of the suspension system is also particularly important in frameless dump vehicles and vehicles designed to carry materials such as coil steel, wherein a heavy load will be completely removed from the vehicle very quickly.
Travel of the suspension system in an upward direction has been most commonly restricted by a stop built into the air spring, usually referred to as a "bumper". Travel of the suspension system in a downward direction (also referred to as "rebound") has traditionally been restricted in a variety of different ways. The most common method utilizes a hydraulic down stop built into the shock absorbers of the suspension system. Although these systems have the benefit of being simple, they were also somewhat limited, with respect to their ability to restrict articulation of the suspension. In severe applications, the hydraulic stop may not be sufficient to handle the loads imposed on it.
In order to provide additional strength to resist axle travel and bottoming out of the shock absorber during rebound, the prior art moved to the use of supplementary devices added to the shock absorber or suspension system itself. External chains and/or cables have been connected between the vehicle chassis and the axle or suspension beam. These devices, however, also suffered from a number of drawbacks.
First, many of these devices, although structurally strong, were too rigid, and, therefore, did not act to absorb or dissipate the vertical forces encountered, but rather allowed translation of a great percentage of those forces into connecting elements and other components of the suspension system. Secondly, all of these "add-on" devices required additional fasteners, brackets, mountings or other connecting elements to be added to the suspension system. These additional elements added additional weight to the vehicle in multiples of two or more, depending upon the number of wheels of the vehicle. This reduced the amount of weight that could be carried by these vehicles under federal and state restrictions by the same amount, thereby reducing profitability of each vehicle trip. Thirdly, known energy-absorbing limiting devices were not constructed as endless loops, and, therefore, had potential weak points on the devices themselves, and also presented only a single flexible band connected between the frame and the suspension team or axle.